Preflight missing Access-Control headers

[adiba]

With the die(); statement on this line https://github.com/Cockpit-HQ/Cockpit/blob/develop/index.php#L134
the access-control headers, which would be set at the 'before' event (in the lines above), are not sent out because 1) they are only set on the $apps response object and 2) the event doesn't have a chance of being fired.

Removing this line at least sends out the headers correctly.

This is the underlying issue of agentejo/cockpit#1021